1. Field of the Invention
The present invention relates to a data transmission/reception system and data transmission/reception method that transmits and receives data with a server outside a moving vehicle even when the moving vehicle is, for example, a train, an automobile, an aircraft, or a ship that is in motion.
2. Description of the Related Art
Document 1 below describes an information communication system in which an information terminal inside a vehicle can connect to a server on the Internet by way of a wireless communication network. In the information communication system that is described in Document 1, an on-board information communication system that is inside the vehicle, an access point such as a wireless LAN that is installed along the route, and a server are connected by way of the Internet.
Document 1: Japanese Patent Laid-Open Publication No. 2002-236632 In the information communication system that is described in Document 1, a user operates the terminal of the on-board information communication system to apply instructions for transmitting and receiving data. In accordance with the user's operations, the on-board information communication system transmits data that have been instructed by the user to the server by way of an access point or a telephone network and the Internet. The server transfers the data to the on-board information communication system by way of the access point or telephone network and the Internet. In the information communication system that is descried in Document 1, an on-board information communication system is able to transmit and receive data even in a moving environment by using either a route-side access point or a telephone network.
In Document 2 described below, a service-providing system is described that uses an on-board server that is installed inside a vehicle as a relay server to connect to a server on the Internet by way of the Internet and a wireless communication network that uses, for example, satellite communication.
Document 2: Japanese Patent Laid-Open Publication No. 2001-222603
In the service-providing system that is described in Document 2, an on-board terminal that is used by a user, an on-board server, an on-board wireless unit, and a transmitter-receiver are established in the vehicle. In addition, the on-board transmitter-receiver is connected to the transmitter-receiver of an information-providing system by way of a wireless communication network. The information-providing system is connected to the servers of, for example, various shops and restaurants by way of the Internet.
In the service-providing system that is described in Document 2, in accordance with the operations of the user, the on-board terminal uses the on-board server as a relay server to access the information-providing system by way of a wireless communication network. The user can then use various services of servers on the Internet while in a vehicle such as a moving train.
The information communication system that is described in Document 1 assumes a constant connection and a real-time connection, and this system is therefore not suited to the transmission and reception of data between a server that is outside the moving vehicle and a moving vehicle that is traveling at high speed, such as an aircraft, bullet train, or TGV, in which communication is easily interrupted. In addition, transmission and reception of data is not possible between a server that is outside a moving vehicle and a moving vehicle that is traveling in areas that cannot be reached by radio wave, such as a subway train or a ship. When a portable telephone network or PHS network is used to communicate with a server that is outside a moving vehicle, the data communication rate is limited and such a system is therefore not suitable for transmitting and receiving a large volume of data.
The service-providing system that is described in Document 2 also assumes a constant connection and is therefore not suited to the transmission and reception of data between a server that is outside a moving vehicle and from within a moving vehicle that is moving at high speed or a moving vehicle that is traveling in a location that cannot be reached by radio wave. For example, communication is not possible between a moving vehicle and the outside when the moving vehicle is traveling at high speed or when the moving vehicle has entered an area that cannot be reached by radio wave such as a tunnel, and the transmission and reception of data in accordance with a request from the on-board terminal therefore becomes impossible. In particular, when communication is interrupted during the transmission and reception of large volume of data, the data download or data upload process must be repeated from the start. In addition, the reliability of transmission and reception of data is low because the on-board server is merely a relay server, and this system is therefore not suited to the transmission and reception of important data.